It is nearly two hours before dawn on a recent morning, and the hunters, three buddies from Ohio, are upbeat as they load their shotguns onto Adam Smith’s boat in Winthrop. They have been planning this trip for a year.

It’s as foggy as foggy gets, which is not great for spotting eider, the majestic arctic sea ducks that have drawn the men all the way from the Midwest to hunt them in their peak plumage as they winter in Boston Harbor. But the air temperature is in the mid-30s, and that is pretty good for sea duck hunting season, which runs from early October to the end of January in Massachusetts.

But as Smith, a hunting guide from Ipswich, steers his 24-foot skiff through the fog in Boston Harbor, the temperature of the water below his boat is also in the mid-30s.

And that is more than a problem. That is a death sentence.

Two recent cases have highlighted the inherent dangers of duck hunting in coastal Massachusetts, where the seafowl arrive just as water temperatures plunge into the danger zone.

Last Sunday, the body of 21-year-old Brown University student Dana Dourdeville was found washed ashore in Falmouth, nearly two weeks after he went missing while duck hunting in a kayak off Fairhaven on New Year’s Eve.

David L. Ryan/Globe Staff

Jim Wolfe (from left), Greg Pollauf, and Scott Bettinger looked over the ducks they had hunted.

On Jan. 7, two duck hunters died, and another barely survived, when their 12-foot skiff capsized in choppy waters on the Westport River.

“This time of year, if you go in the water, the likelihood is that it’s going to be a fatal event,” said Dr. N. Stuart Harris, the chief of the division of wilderness medicine at Massachusetts General Hospital. “If you’re not wearing specialized equipment, such as a dry suit or a survival suit, you just don’t have a chance. That the one hunter got out of the water is fairly remarkable.”

The Coast Guard requires dry suits for all its on-water personnel when water temperature drops below 50 degrees, but hunters say the dry suits — which feature thick rubber gaskets at the neck and wrists to keep water out — are hot and cumbersome, making it difficult to shoot.

Smith — who spent 30 years as a commercial fisherman before opening his hunting guide business, Perfect Limit — said that safety is a simple matter of paying attention to the weather and having a solid boat.

On the day the hunters died in Westport, there were high winds and choppy waters, so it was one of two days this hunting season that Smith did not go out on the ocean. Instead, he took his clients hunting on a marsh.

As he steers his boat slowly through Boston Harbor, dawn is still a long way off when Smith drops the three buddies from Ohio at the end of a rocky jetty just off the Deer Island Wastewater Treatment Plant and begins laying out a few dozen plastic duck decoys in the water surrounding them. The hunters are after trophies, not food, “because sea ducks taste like [expletive],” one of the men said. One of them is an amateur taxidermist, and the male ducks have a gorgeous, thick, white-and-black coat this time of year that he’s hoping to mount.

As the dawn begins illuminating the fog, the men get into position on the slick rocks, taking the occasional spray from the rising tide, but no one falls in, which is a good thing.

During the first minute in such icy water, the body goes through something called cold shock response, an involuntary mixture of gasping and hyperventilating that can be immediately deadly if the head is submerged, forcing the victim to take in water as the person gasps. The shock can also lead to a cardiac episode. Many do not survive the first minute.

Lieutenant Bryan Swintek, who oversees the Coast Guard command center in Woods Hole and was involved with the attempted rescues in Fairhaven and Westport, said that people should be aware of the 1-10-1 rule in cold water.

For the first minute, the goal is to get the breathing under control. After that, the body will have 10 minutes of functional movement when hands and feet should still be usable.

After that, the extremities will shut down as the body focuses on keeping the core alive, but a person should still have one hour of survival time in the water.

But that is only if the victim is wearing a life jacket that can allow a person to tread water. “The difference between functional time and survival time is what the life jacket buys you,” Swintek said.

David L. Ryan/Globe Staff

“This time of year, if you go in the water, the likelihood is that it’s going to be a fatal event,” said Dr. N. Stuart Harris, the chief of the division of wilderness medicine at Massachusetts General Hospital.

Dourdeville, who went out in a 9-foot kayak, was wearing a life jacket and warm clothes, but he was not wearing any clothing designed for going into the water, Swintek said. The three hunters in the Westport River were similarly dressed in warm clothing for the air temperature, which was just 8 degrees, but nothing specifically designed for the water, said Swintek, and only one was wearing a life jacket.

Swintek said the three men on the Westport River were attempting a 7-minute trip across the river in a 12-foot skiff to a plot of land where they were planning to hunt. They had made the same trip the previous day. But on their fateful trip, the current and the wind were opposing each other, creating steep waves that swamped the boat. Two men, Steven James, 53, of Marshfield and Robert Becher, 55, of Cromwell, Conn., jumped out and tried to swim to shore, but never made it. The third man, Gregg Angell, 51, a physician from Westport, stayed with the boat a bit longer and made it to shore after he went into the water.

For those who go out on the ocean in the winter in New England, dry suits remain a rarity, said Joe Curcuru, manager of Fisherman’s Outfitter in Gloucester, which supplies many people who work the water year-round. “You’re not going to be wearing a survival suit or a dry suit when you’re fishing or hunting,” he said. “They’re too big and bulky, and they’re bright orange, and hunters want to be camouflaged. The only thing you can do is be smart and try to stay out of the water in the first place.”

On this day in Boston Harbor, things go smoothly for the hunters. Not so much for the ducks. The decoys work, and as the sun turns the fog milky white, duck after duck comes in for a soft landing next to its plastic cousins. In short order, each of the men shoots his daily allotment of four eider, including a few they describe as “studs” that will make great wall décor. After each round of shooting, Smith’s son, Adam Smith Jr., hangs from the bow of the boat and scoops them into a net.

When the day was done and they had shot all they could, Smith picked the hunters up from the slippery jetty and headed back to shore.

“This is what I like, all the guys safe and back in the boat,” Smith said as they boarded his double-bottomed fiberglass skiff. “This boat is unsinkable.”

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